Method and device for separating gas mixtures formed above liquids

ABSTRACT

In a method for separating a gas mixture above a liquid a separating device with a gas separation membrane having retentate side and a permeate side is employed. A vacuum at the retentate side of the gas separation membrane and a vacuum at the permeate side of the gas separation membrane are provided. The gas mixture, resulting from transferring a liquid from one storage container to another container upon contact with the surroundings, is fed to the retentate side of the gas separation membrane by the vacuum present at the retentate side and the permeate side. The flow volume per time unit of the gas mixture fed to the separating device is greater than a flow volume per time unit of the liquid being transferred. On the retentate side of the gas separation membrane a gas-diminished retentate is generated and on the permeate side of the gas separation membrane a gas-enriched permeate is produced. The flow volume per time unit of the permeate is equal to the flow volume per time unit of the liquid being transferred.

BACKGROUND OF THE INVENTION

The invention relates to a method for separating gas mixtures formedabove liquids, especially hydrocarbon gas mixtures, by using aseparating device comprising a gas separation membrane, on the retentateside of which a mixture (retentate) diminished in one or more componentsand on the permeate side of which a mixture (permeate) enriched by oneor more components can be generated, as well as to a device forperforming this method.

It is known that, for example, upon filling of containers with liquids,gases, respectively, gas mixtures comprised of the components of theliquid are formed directly at the filling location. In the past, thisgas, respectively, gas mixture, resulting from processes governed bynatural laws, has been released in most situations into the surroundingsin an uncontrolled manner, for example, during filling of gas tanks ofmotorized vehicles at gas stations directly into the air. Theuncontrolled release of gas, respectively, gas mixtures during suchtransfer, respectively, refilling operations has two considerabledisadvantages. On the one hand, a considerable amount of the liquid isreleased in a gaseous form into the surroundings, which results in aconsiderable economical disadvantage, and, on the other hand, theenvironment as well as the person performing the transfer, respectively,filling operation is exposed to considerable amounts of noxious gases.

For eliminating these considerable disadvantages it has been suggestedamong other things due to regulatory mandates, for example, for thefilling of tanks of motorized vehicles, to provide the so-called pumpnozzle, from which the fuel exits in order to be filled into themotorized vehicle, with a sealing sleeve that encloses the tank socketand parts of the nozzle whereby the transition of the tank socket to thenozzle is sealed relative to the surroundings. Via this sealing sleevethe gases formed during the filling operation are enclosed relative tothe surroundings and returned into the tank. In this manner it is to beensured that during filling of the tank of a motorized vehicle, which isapplicable in the same manner in general to other containers to befilled, the gases respectively, gas mixtures formed during transfer,respectively, filling cannot exit from the tank but instead are recycledwithin a closed system. In this context, a filter which is, in general,provided within a tank vent of any liquid containing tank and is, forexample, in the form of an active carbon filter designed to reduce theventing loss of such tanks, serves to absorb the gases that are formedwithin the tank, respectively, container of a motorized vehicle. Thegoal is to return the displaced gas volume from an operating liquid tankinto a storage tank from which the liquid has been transferred into theoperating liquid tank. This is also referred to by the term "gasshuttling". Gas shuttling is demanded by law in different countries andcomprises the installation of a small active carbon container withinmotorized vehicles for reducing the venting losses as well as for gasshuttling at gas stations.

It is an object of the present invention to provide a method and adevice of the aforementioned kind with which the last mentioned systemscan be improved such that an even more effective return of gases,respectively, gas mixtures into the liquid container is possible wherebythe method shall be performed with simple means and the device forperforming the method should be cost-effective and essentiallymaintenance-free so that the method and/or the device can be used inlarge numbers, for example, at any suitable fuel pump or as a centralunit of a gas station for motorized vehicles etc., so that thereby theenvironmental impact and the health risk to the person performing therefilling operation can be reduced to limits that are safe with respectto the environment and health.

SUMMARY OF THE INVENTION

This object is solved according to the inventive method by providingthat the flow volume per time unit of the gas mixture to be separatedand fed to the separating device by vacuum produced at the retentate andpermeate side, which gas mixture is formed during the transfer operationof the liquid upon contact with the surrounding gas, is greater than theflow volume per time unit of the liquid transferred during the transferprocess and the flow volume per time unit of the generated permeate isequal or smaller than the flow volume per time unit of the liquid duringtransfer.

In this manner it is advantageously ensured that the stable layer of amixture of gas and air formed above the liquid level of a container ortank, in which, for example, fuels such as gasoline etc. are stored, ismaintained in a predetermined relation not to be disturbed so that thisrelation is inventively not disturbed and the thus operated gas returnsystems with vacuum assistance are not subjected to any reduction oftheir effectiveness.

Accordingly, the inventive method for separating a gas mixture above aliquid is primarily characterized by the steps of:

employing a separating device with a gas separation membrane having aretentate side and a permeate side;

producing a vacuum at the retentate side of the gas separation membraneand a vacuum at the permeate side of the gas separation membrane;

feeding the gas mixture, resulting from transferring a liquid from onestorage container to another container upon contact with thesurroundings, to the retentate side of the gas separation membrane bythe vacuum present at the retentate side and the permeate side;

providing a flow volume per time unit of the gas mixture fed to theseparating device that is greater than a flow volume per time unit ofthe liquid being transferred;

generating a gas-diminished retentate on the retentate side of the gasseparation membrane and generating a gas-enriched permeate on thepermeate side of the gas separation membrane; and

providing a flow volume per time unit of the permeate that is equal tothe flow volume per time unit of the liquid being transferred.

The method may further comprise the step of lowering the pressure of theretentate relative to pressure of the gas mixture.

In another embodiment of the invention, the method further comprises thestep of returning the permeate to the storage container.

Preferably, the method comprises the step of releasing the retentateinto the surroundings.

Advantageously, the suction pressure of the gas mixture is adjusted to apredetermined value before the gas mixture enters the separating device.

The present invention also relates to a device for separating a gasmixture above a liquid characterized by:

a separating device with a gas separation membrane having a retentateside and a permeate side, the separating device receiving a gas mixture,resulting from transferring a liquid from a storage container to anothercontainer upon contact with the surroundings;

a first pump connected to the retentate side for generating a vacuum anda second pump connected to the permeate side for generating a vacuum,wherein from the gas mixture a gas-diminished retentate is produced onthe retentate side and a gas-enriched permeate is produced on thepermeate side by the vacuum at the retentate side and the permeate side;and

the first and the second pumps adjusted relative one another such that aflow volume per time unit of the gas mixture fed to the separatingdevice is greater than a flow volume per time unit of the liquid beingtransferred and such that a flow volume per time unit of the permeate isequal to the flow volume per time unit of the liquid being transferred.

Preferably, a feed line is connected between a location of transfer ofthe liquid and the separating device, the feed line comprising a valve.

Advantageously, the second pump has a suction side connected to thepermeate side of the separating device and a blower side connected to aliquid receptacle.

The first pump preferably has a suction side connected to the retentateside of the separating device and a blower side connected to thesurroundings.

The first pump is expediently connected to a venting space of thestorage container.

Advantageously, a means for adjusting the pressure of the gas mixturefed to the separating device is provided.

According to an advantageous embodiment of the invention the relation ofvolume of the returned gas mixture and the transferred liquid is in anarea of 1 to 1.05.

In order to enable in a simple and directed manner a removal of the gasmixture directly at the location of transfer, respectively, refilling ofa container with liquid, it is advantageous to lower the pressure of thepermeate relative to the gas mixture to be separated wherebyadvantageously also the pressure of the retentate relative to thepressure of the gas mixture pressure to be separated can be reduced.Accordingly, in a directed manner, the pressure ratio for the separationof the gas mixture in the separating device comprising a gas separationmembrane is used in order to generate within the area of transfer such avacuum that the surroundings of the filling socket of a container ortank that is loaded with gases or gas mixtures is completely suckedfree.

Preferably, the retentate is returned to a liquid supply from which theliquid has been removed during the transfer process, for example, anunderground storage tank of a gas station etc.

The retentate that is only weakly contaminated with gas to be separatedis advantageously released into the surroundings. However, it may alsobe expedient not to release the retentate directly into thesurroundings, but instead to guide the retentate into the venting spaceof a liquid container so that, for example, a deficiency in the gasvolume of the liquid container can be compensated with this measure.

It is furthermore advantageous to adjust the suction pressure of the gasmixture to be separated to a predetermined value before entering theseparating device.

With a device for performing the method the inventive object is solvedby arranging a pumping device for generating a vacuum within theseparating device on the retentate side as well as on the permeate sidewhereby the pumping devices are adjustable such that the flow volume pertime unit of the gas mixture formed during the transfer process of aliquid upon contact with the surrounding gas and to be separated and fedinto the separating device is greater than the flow volume per time unitof the liquid transferred during the transfer process and that the flowvolume per time unit of the produced permeate is the same or smallerthan the flow volume per time unit of the liquid transfer during thetransfer process.

The advantage of the inventive device is that the pumping devices on theretentate side and on the permeate side are adjustable in theiroperating characteristics such that within a range of their minimum loadup to reaching their full load always the same separating result can beinsured for the separating device with gas separation membrane, wherebyin a simple manner the flow volume per time unit relation can beadjusted continuously so that the allowed ratio of gas, respectively,gas mixture to flow volume of liquid that has been transferred is notsurpassed within the container, respectively, tank. Thus, in a simplemanner, it is insured that a stable layering of gases, respectively, gasmixtures above the liquid level within the container, respectively, tankis not disturbed.

In general, it is possible with a suitable selection of pumping devicesto maintain the flow volume per time unit relation continuously betweenminimal load and maximum load. Advantageously, a control valve isarranged within a feed line for the gas mixture from the location oftransfer to the separating device because such a control valve is easilyadjustable. With it the ratio of gas mixture to be removed from thelocation of transfer to the transferred amount of liquid can beadjusted, sometimes easier than by controlling the pumping devices.

The pumping device for the permeate is advantageously connected with itsblower side to a liquid container into which the regained permeate isreturned, while the retentate leaving the pumping device isadvantageously released into the surroundings. The available pressure ofthe pumping devices, which are preferably vacuum pumps, at the blowerside is so great that no additional pump means are required in order toprovide for the aforementioned feed of the retentate as well as thepermeate into the surroundings, respectively, into the liquid container.

It can also be advantageous that the pumping device for the retentate isconnected to the venting space of the liquid container so that, forexample, a deficiency in gas, respectively, gas mixture volume withinthe liquid container can be compensated by the retentate coming from theseparating device.

Finally, in another advantageous embodiment of the device, the suctionpressure of the gas mixture to be separated and fed to the separatingdevice may be adjustable with a control valve.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in detail with the aid of thefollowing only schematic drawing in context with one embodiment. Thedrawing shows:

In the form of a diagrammatic connection the individual elements of thedevice in cooperation with a fuel pump for refueling a motorized vehiclewith liquid fuel and the cooperation of the device with a liquidcontainer from which the fuel is supplied.

DESCRIPTION OF PREFERRED EMBODIMENTS

The device 10 represented in the only figure comprises substantially aseparating device 13 comprising a gas separation membrane whichseparating device 13 performs the separation of a gas mixture 12 in amanner known per se into a retentate 14 and a permeate 15, for exampleby gas permeation. Since these separating methods with which suchseparating devices 13 operate are known in general, they will not beexplained here. The inlet of the separating device 13 is connected via afeed line 19 with the supply hose 24 of a filling station for a liquid11 whereby the liquid 11 is supplied from a liquid container 22 via asuitable connecting line to the filling station 25 with non-representedpumping means for pumping the liquid 11. The hose 24 is a so-calledcoaxial hose which is able to supply the gas mixture 12 to be separatedas well as the liquid 11 for refilling the tank of a motorized vehicle26; compare the only figure.

Within the feed line 19 for feeding the gas mixture 12 from the locationof transfer 30 to the separating device 13, a valve in the form ofcontrol valve 21 is arranged which will be described in detail infra.Downstream of the separating device 13 pumping devices 16, 17 in theform of vacuum pumps are arranged on the retentate side 14 as well as onthe permeate side 15 for generating a vacuum at the retentate,respectively, permeate side of the separating device 13. The pumpingdevice 17 for the permeate 15 is connected with its blower side to theliquid container 22, while the retentate 14 leaving the pumping device16 can be connected, if desired, to a venting line 27 which, in general,connects the venting space 23 of a liquid container to the surroundings,(atmosphere) respectively, the surrounding gas which is air 18.

Upon operation according to the inventive method the device 10 operatesas follows:

The filling nozzle 28 provided at the free end of the supply hose 24 isinserted into the tank socket (not represented in detail) of a tank of amotorized vehicle 26. The filling nozzle 28 is provided within thedirect vicinity of its outlet opening for the liquid 11 with anon-represented suction nozzles, respectively, suction openings thatprovide for the removal of the gas mixture 12 that is produced duringthe transfer of the liquid 11 upon contact with the surrounding gas 18,here surrounding air. With the aid of the two pumping devices 16 and 17the gas mixture is guided during transfer of liquid 11, upon actuationof the transfer valve of the filling nozzle 28, through the supply hose24 in the form of a coaxial hose and via the control valve 21 to theseparating device 13. The two pumping devices 16, 17 provide such agreat pressure reservoir for the inventive function of the device 10that no additional measures for providing sufficient feed of the gasmixture 12 to the separating device 13 must be provided. In order to beable to maintain a substantially constant vacuum within the area of thetransfer location 20, i.e., within the area of the transfer of theliquid 11 into the socket of the tank of a motorized vehicle 26, thecontrol valve 21 is provided, i.e., with this control valve 21 aconstant vacuum can be maintained.

With a suitably selected pumping power of the pumping devices 16, 17 inconnection with the control valve 21, it is insured that the flow volumeper time unit of the gas mixture, which is formed during the transfer ofthe liquid 11 upon contact with the surrounding gas 18 and conveyed bythe vacuum produced at the permeate and retentate side, is greater thanthe flow volume per time unit of the liquid 11 transferred during thetransfer process and that the flow volume per time unit of the generatedpermeate 15 is identical or smaller than the flow volume per time unitof the liquid transferred during the transfer process. The ratio ofvolume of gas mixture 12 to be separated at the inlet and the volume ofliquid transferred from the liquid container 22 is in the range of 1 to1.05.

The permeate 15 exiting the separating device 13 is returned from theexit side of the pumping device 17 into the liquid tank 22. Theretentate exiting the separating device 13 via the pumping device 16,i.e., in the present case air with only a minimal degree ofcontamination with components of the liquid 11, is released into thesurroundings 18, respectively, the surrounding gas, i.e., air, or isreturned into the venting space 23 of the liquid container 22 in orderto compensate a deficiency in gas volume within the liquid container 22.

With the aid of a model calculation the inventive method is explainedfor two operational stages.

    ______________________________________                                                   Flow               Flow                                                       volume             volume                                                     (during            (standard                                                  operation)                                                                             Pressure  condition)                                                 [m.sup.3 /h]                                                                           [mbar]    [m.sup.3 /h]                                    ______________________________________                                        11    gasoline   1.67       --      --                                        19    vapors/air 2.22       900     2                                         190   vapors/air 8.62       116     2                                         14    retentate  6.1         66     0.401                                     140   retentate  0.401      1013    0.401                                     15    permeate   100         16     1.599                                     150   permeate   1.599      1013    1.599                                     11    gasoline   8.33       --      --                                        19    vapors/air 11.11      900     10                                        190   vapors/air 22.62      442     10                                        14    retentate  6.1        392     2.41                                      140   retentate  2.41       1013    2.41                                      15    permeate   100         76     7.59                                      150   permeate   7.59       1013    7.59                                      ______________________________________                                    

The inventive method and the inventive device 10 can also be used forseparating other gas mixtures, for example, permeate gas mixtures forwhich at different flow volumes a uniform separation is desired.

The present invention is, of course, in no way restricted to thespecific disclosure of the specification and drawings, but alsoencompasses any modifications within the scope of the appended claims.

We claim:
 1. A method for separating a gas mixture above a liquid, saidmethod comprising the steps of:employing a separating device with a gasseparation membrane having a retentate side and a permeate side;producing a vacuum at the retentate side of the gas separation membraneand a vacuum at the permeate side of the gas separation membrane;feeding the gas mixture, resulting from transferring a liquid from onestorage container to another container upon contact with thesurroundings, to the retentate side of the gas separation membrane bythe vacuum present at the retentate side and the permeate side;providing a flow volume per time unit of the gas mixture fed to theseparating device that is greater than a flow volume per time unit ofthe liquid being transferred; generating a gas-diminished retentate onthe retentate side of the gas separation membrane and generating agas-enriched permeate on the permeate side of the gas separationmembrane; and providing a flow volume per time unit of the permeate thatis equal to the flow volume per time unit of the liquid beingtransferred.
 2. A method according to claim 1, further comprising thestep of lowering the pressure of the retentate relative to pressure ofthe gas mixture.
 3. A method according to claim 1, further comprisingthe step of returning the permeate to the storage container.
 4. A methodaccording to claim 1, further comprising the step of releasing theretentate into the surroundings.
 5. A method according to claim 1,further comprising the step of adjusting the suction pressure of the gasmixture to a predetermined value before the gas mixture enters theseparating device.
 6. A device for separating a gas mixture above aliquid, said device comprised of:a separating device with a gasseparation membrane having a retentate side and a permeate side, saidseparating device receiving a gas mixture, resulting from transferring aliquid from a storage container to another container upon contact withthe surroundings; a first pump connected to said retentate side forgenerating a vacuum and a second pump connected to said permeate sidefor generating a vacuum, wherein from the gas mixture a gas-diminishedretentate is produced on the retentate side and a gas-enriched permeateis produced on the permeate side by the vacuum at said retentate sideand said permeate side; and a means for adjusting a pumping power ofsaid first and said second pumps relative one another such that a flowvolume per time unit of the gas mixture fed to the separating device isgreater than a flow volume per time unit of the liquid being transferredand such that a flow volume per time unit of the permeate is equal tothe flow volume per time unit of the liquid being transferred.
 7. Adevice according to claim 6, further comprising a feed line connectedbetween a location of transfer of the liquid and said separating device,said feed line comprising a valve.
 8. A device according to claim 6,wherein said second pump has a suction side connected to said permeateside of said separating device and a blower side connected to a liquidreceptacle.
 9. A device according to claim 6, wherein said first pumphas a suction side connected to said retentate side of said separatingdevice and a blower side connected to the surroundings.
 10. A deviceaccording to claim 9, wherein said first pump is connected to a ventingspace of the storage container.
 11. A device according to claim 6,further comprising a means for adjusting the pressure of the gas mixturefed to said separating device.